Mounting system for elements of television projectors



D. w. EPSTEIN 2,455,476 MOUNTING SYSTEM FER ELEMENTS OF EELEVISIONPRQJECTORS Dec. 7, 1948.

Filed July 20, 1945 IVNVENTOR. Q4140 WfPJTf/M ATTORNEY Patented Dec. 7,i948 MOUNTING SYSTEM TELEVISION P FOR ELEMENTS OF ROJECTORS David W.Epstein, Princeton, N. 3., assignor to Radio Corporation of America,

of Delaware a corporation Application July 20, 1945, Serial No. 606,21511 Claims. (Cl. 178-75) The present invention relates to a system forprojecting images produced by the image producing device of a televisionreceiver, and more particularly, though not necessarily exclusively, toan organization of elements comprising a spherical mirror, an asphericzone plate, and the image producing surface of a cathode ray tubeassociated together in proper alignment whereby to project an image upona screen which may be readily located in a preferred position withrespect to this organization. The invention is also concerned in one ofits aspects with a method of locating the several parts of theorganization with respect to each other in a novel manner.

In. United States Patent No. 2,273,801, granted February 1'7, 1942, toD. O. Landis, there is disclosed an arrangement whereby a sphericalmirror or reflecting surface is arranged to direct and focus light raysforming the enlarged television image upon a viewing screen with the aidof an aspheric correcting plate or correcting lens. The organization ofessential optical parts shown in this Landis patent must, for bestresults, be aligned and spaced in a certain definite relationship withinvery close tolerance limits, and the primary aim of the invention is toprovide methods of and means for so aligning and spacing the essentialoptical parts. This important aim of the invention is carried out in anillustrative embodiment thereof which will be described in detailhereinafter in such a way that commercial requirements may be met forquantity production of television receivers of the projection type.

The second important aim or object is to provide a novel method of andmeans for aligning and positioning the optical parts of the imageprojection system of a television receiver within predictable tolerancelimits.

Still another object is to provide for locating a cathode ray imageproducing tube in a television receiver with respect to a sphericalreflector and its associated aspheric zone plate with a sufficientdegree of accuracy.

A still further object is to provide a novel casing or housing forsupporting and/or containing the optical elements of an image projectionsystem for a television receiver.

A still further object is to produce an image projector in whichalignment of the parts in correct optical relationship is automatic uponassembly of the parts and depends primarily on manufacture of principalsupporting parts in accordance with the invention and not upon criticaladjustments after assembly.

A still further object is to provide a novel positioning arrangement forthe cathode ray tube in a television receiver projection system.

Other objects and advantages of the invention will, of course, becomeapparent and immediately suggest themselves to those skilled in the artto which the invention is directed from a reading of the followingspecification in connection with the accompanying drawings in which:

Fig. l is a geometrical representation of the relationship of theprincipal parts of a projection optical system correlated in accordancewith the invention;

Fig. 2 is a view in sectional elevation of a projection optical systemin accordance with the ininvention showing details of the several partsthereof, the section being taken on line 2-2 of Fig. 3; and

Fig. 3 is a top plan view in section of the apparatus of Fig. 2, thesection being taken on line 3-3 of Fig. 2.

Referring to Fig. shows the general 2 of the drawings, whichorganization oi'a television projection system embodying the inventionin one of its forms, an image producing tube ill, which has a televisionimage produced on its luminescent target l2, projects the televisionimage along an optical path conventionally represented at M toward areflecting element It which has a spherical reflecting surface 2!. Theimage which has been projected upon the reflecting surface 2| is thenreflected therefrom along the optical path conventionally represented at23 and it toward a suitable viewing screen (not shown) At anintermediate point in the optical path an aspheric zone plate 26 (alsotermed a correcting plate or correcting lens) is positioned to receivethe light reflected from the reflecting surface 2|. The aspheric zoneplate 26 is arranged externally to the light path from the tube to thereflector and is axially aligned with each. This zone plate is arrangedto correct for any spherical aberrations introduced into any of thelight rays by the curved reflecting surface 2! of the member l8 so thata sharply focused reproduction of the image developed on the fluorescentor luminescent target area produced on the previously mentioned viewingscreen. The aspheric zone plate 26 has a central opening 29 for thepurpose of accommodating the tube neck 3| and, if desired, thedeflecting yoke (not shown) for producing deflection of the cathode raybeam within the tube Ill. The curved target face l2 of the tube I!)rests upon a circular edge 32 provided by a ring 33. In place of thering 33, a series of points, no less than three; may be arranged tofurnish location and support of the tube face l2 as will be pointed outhereinafter, The target face 12 of the tube ill will be approximatelyspherical, or exactly spherical, and

I2 of the tube It is its center is indicated at 34 on Fig. 2. Adiscussion of contour of the target face is to be found in thepreviously mentioned Landis patent, No. 2,273,801. The zone plate 26 aswell as the ring 33 is located and-supported through the agency of acylindrical member 36. The more detailed features of the cylindricalmember 36 as well as details of the mounting of the ring 33 will bediscussed more in detail hereinafter.

Reference will now be had to Fig. 1 for an explanation of therelationship between the parts of Figs. 2 and 3 which provides foraccurately determining the respective positions of these parts. In Fig.1, a segment of a sphere is shown as an arc, for convenience, whichcorresponds to the reflecting surface 21 of Fig. 2 and is so marked. Acylinder marked 36 is also shown which corresponds to the cylindricalmember 36 of Fig. 2. From a consideration -of the simple geometricalfigures shown in Fig. '1, it will be seen that with the circular edge 38of the cylinder 36 resting on the spherical curve of the segment 2|, thecenter of the sphere '39 must necessarily noon the geometrical axis-ofthe cylinder provided that the lower edge 38 of the cylinder is planarand normal to the axis of the cylinder. In a projectionsystem of thetype presently under consideration, the most important reference pointis the center of the spherical reflecting surface, but it is diflicultto locate and difiicult to use for the purpose of locating otherelements of the system. 'By the novel construction of the inventionillustrated in Fig. l of the drawings, it will be seen that th'ecenterof curvature 39 of the spherical surface lies at a point on the axisofthe cylinder.

It will be understood that in place'of the cylindrical member "36 shownby Figs. 2 and 3 and represented in Fig. 1, any surface of revolutionwith an axis of symmetry such as a frustrum of a cone or system ofelements of such a figure such as a tripod will serve thepurpose. Thecenter of the aspheric zone plate 26 must be located at the center'ofcurvature of the reflecting surface 2 Land for uniform fieldillumination, the -axis of symmetry of the correcting lens preferablycoincides with the "circular boundary of the portion of the reflectingsurface 21 which is used for projection purposes. In Fig. 1 thisboundary may be taken asset by the diameter of the cylindrical figure36.

The considerations in connection with Fig. 1 so far discussed insurethat the aspheric zone plate will be automatically lined up laterally asit is located symmetrically with respect to the axis of the cylinderprovided that the resting surface for the .aspheric zone plate, whichmay be represented by the top M of the cylinder, is planar, parallel andcoaxial with the circle 38. The rest ing surface diagrammatically shownon Fig. 1 is indicated by reference character 4| in Fig. 2 of thedrawings. The shoulder 42 positions 'the'plate 26 concentric with thecircle 38. A concentric opening 43 provides a light aperture and admitsthe tube l 0. Axial alignment of the aspheric correcting plate so thatit is at the center of curvature 39 of the surface 2| is obtained byusing the correct length of the cylinder 36 which is easily calculatedfrom the radius of curvature R of the reflecting surface 2| and radius aof the cylinder. Thus, if his the height of the cylinder, then, fromeither right triangle of Fig. 1

The substantially exact location of the center of curvature 39 of thereflecting surface 2-! within the surface boundaries of the correctinglens 26 and along its axis may be fixed by reference to the formulato/N. In this formula, to is indicated on the drawing and N is the indexof refraction of the material composing the correcting plate or lens 26.For the special case shown, to/N is also indicated. The distance to/N ismeasured from the fiat side of the correcting lens when this flat sidefaces the reflecting surface 2| and the distance determined from theformula is the distance from the apex of the correcting lens when itscurved side faces the mirror.

The location of the target face [2 of the tube 16 with respect to otherelements in the projection system is important, and locating andpositioning the tube I0 generally will be discussed in connection withFig. 2 of the drawings and the more detailed features of the inventionshown therein. However, the plane of the :ring'33 must be parallel toand coaxial with the .lens holder circle 4! for best results.

Referring again to Fig. 2, one of the very important conditions to befulfilled, in addition to the one involving the center :of curvature 39of the reflecting surface 21, is the location of the tube target face l2so that its center of curvature is on the axis-of symmetry of theaspheric correcting plate 26. Also, for uniform illumination over thefield, the axis of symmetry of the periphery of the tube face and the:axis of the symmetry of the correcting plate should preferablycoincide. Moreover, the tube target face should be located at thecorrect axial distance :from the reflecting surface 2| or from the.aspheric zone plate 26 for focusing.

The points of reference for locating the tube face may be the *wall ofthe cylindrical member 36 or the top member 44 of the cylinder which isrecessed to provide the previously mentioned surface M for supportingthe a'spheric'zone plate .26. For purposes of illustration, referencepoints on this topmem-ber 44 or izonezplate holder have been selectedfrom which to locate the tube face, and this is accomplished in theillustrative example by locatin two holes '46 and 4! :at diametricallyopposite points. A bracket 5| carried :at the end of a rod 52 serves asa principal support for the ring 33. The general shape of this bracketis such that it is resistant to bending stress caused by the weight ofthe tube. For example, it may be generally triangular :as shown. The rod52 is slidable in the hole 46 and is adjustable axially and held in aselected position by a nut 53 upon its reduced threaded end 54. The.ring 33 is provided with a lateral extension 56 which is dowelled tothe bracket/5i for location purposes by dowel pins 51. Securing means inthe form of screws 58, for example, hold the extension 56 to the bracket5|. The ring 33 is provided with a diametrically opposite extension 59which is secured to a bracket 63 by a screw 64., for example. One ormore dowel pins 66 -preserve the desired alignment of the bracket :63with respect to the extension 59. The bracket 63 is slotted as indicatedby reference character 69 to accommodate the end of aguide .12 which iscentered with respect to the hole 41 by being formed upon or carried atthe end of a rod 14, secured in the hole 41 by suitable means such as anut 16.

From the parts thus far described, it will be seen that the reflectingsurface 21,, the aspheric zone plate 26, and the target face 12 of thetube ID are all positioned in the desired relationship within necessaryand/or desired limits of accuracy. The organization. comprising thethree arts just enumerated may be mounted in any lesired manner in atelevision cabinet, or the ike (not shown). For example, the reflectinglenient is may have a centrally located aperture vo receive a mountingrod, mounting bolt, or the .ike, inasmuch as a limited area at thecenter of ;his element is usually rendered non-reflective. Preferably,however, and in accordance with the invention in a preferred form, thecylindrical member 36 is clamped upon the reflecting sur face 2! and thereflecting member [8, in turn, is clamped in a desired position by meansof a ring '58 provided wth a flange 19. An annular projection 3!provided on the cylindrical member 36 is apertured as by drilling atintervals to accommodate clamping bolts 83. A gasket or washer 8'6 ofyielding material provides for cushioning the member A8 at its clampingedge.

In accordance with the invention, it will be understood that thecylinder 35 may be so positioned within or upon the housing (not shown)if or the television apparatus or the like that it may be moved bodilyaxially for the purpose of bringing an image produced on the targetsurface l2 of the tube ID into focus upon a suitable screen or the like(not shown) after projection, Where the cylinder 36 is bodily movable asjust stated, the supporting rod 52 may be stationary with respect to thecylinder 36 and the nut 53 will, in that case, be a mere clampingmember. Also, it is within the scope of the invention to manufacture themember H8 in such a way that the refiecting surface 2i is concentricwith the back 92 of the member, in which case the edge 38 of thecylinder 36 may be provided interiorly of the cylinder and contact thesurface 92.

From the foregoing, it will beseen that an optical projection system isprovided in which the parts may be held together in proper relationshipto fulfill above for insuring projection efficiency. To summarize, theseconditions are, first, that the center of the aspheric zone plate 26must be located at the center of curvature of the reflecting surfaceill. The luminescent target face [2 of the tube it] must be located sothat its center of curvature is on the axis of symmetry of the asphericzone plate 26. For uniform illumination over the field, the axis ofsymmetry of the aspheric zone plate should preferably coincide with theaxis of symmetry for the periphery (circle) of the mirror. Theluminescent target area l2 of the tube should be the correct axialdistance from the reflecting surface 2| or from the aspheric zone platefor focusing. The previously mentioned viewing screen (not shown) shouldbe normal to the axis and at the correct throw either by actualalignment or through the medium of a 45 mirror or other device. Thislatter requirement may be fulfilled by design of the cabinet or the likein or upon which the ring 18, or its equivalent within the scope of theinvention, is mounted.

Having now described the invention, what is claimed and. desired to besecured by Letters Patent is the following:

i. The combination with an electron image tube having a surface exposinga target area, of an optical light receiving element having asubstantially spherical surface, a member having means defining a circleresting on said spherical surface whereby the center of curvature ofsaid spherical surface lies on the optical axis of both said member andsaid circle, a correcting plate to receive light reflected from saidsubstantially spherical surface, supporting means for said corseveralconditions mentioned recting plate, means associated with said memher tomaintain said correcting plate coaxial with said circle, and a mount forsaid tube carried by said member and being coaxial with said circle.

3. The combination with an electron image tube having a surface exposinga target area, of an optical light receiving element having asubstantially spherical surface, a member havin means defining a circleresting on said spherical surface whereby the center of curvature ofsaid spherical surface lies on the axis of both said member and saidcircle, a correcting plate to receive light reflected from saidsubstantially spherical surface supporting means for said correctingplate, means associated with said memher to maintain said correctingplate coaxial with said circle, and a mount for said tube upon whichsaid target area exposing surface rests to position said surface withrespect to said light receiving element, said mount being carried bymeans located from said supporting means for the correcting plate. I

4. The combination with an electron image tube having a surface exposinga target area, of an optical light receiving element having asubstantially spherical surface, a member having means defining a circleresting on said spherical surface whereby the center of curvature ofsaid spherical surface lies on the axis of both said member and saidcircle, a correcting plate to receive light reflected from saidsubstantially spherical surface, said member having an end opposite tosaidcircle defining means, said end being provided with a recess coaxialwith the circle defining means, and a mount for said tube coaxial withsaid member.

5. The combination with an electron image tube having a surface exposinga target area, of an optical light receiving element having asubstantially spherical surface, a member having means defining a circleresting on said spherical surface whereby the center of curvature ofsaid spherical surface lies on the axis of both said member and saidcircle, a correcting plate, supporting means for said correcting platefixed to be coaxial with said member, means for supporting said tube bycontacting its target exposing surface, said member having an endopposite to said circle defining means, a pair of diametricallypositioned rods depending from said end, said tube supporting meansbeing substantially rigidly carried by one of said rods, and the otherof said rods serving as a guide to position said tube supporting meanscoaxial with the axis of said member.

6. The combination with an electron image tube having a surface exposinga target area, of an optical light receiving element having asubstantially spherical surface, a member having means defining a circleresting on said spherical surface whereby the center of curvature ofsaid spherical surface lies on the axis of both said member and saidcircle, a correcting plate, supporting means for said correcting platefixed to be coaxial with said member, means for supporting said tube bycontacting its target exposing surface, said member having an endopposite to said circle defining means, said end being provided with acircular recess coaxial with the circle defined by said circle definingmeans, a pair of diametrically positioned rods depending from said end,said tube supporting means being substantially rigidly carried by one ofsaid rods, and the other of said rods serving as a guide to posi- 7 tionsaid tube supporting means coaxial with the axis of said member.

"7. In an image projection system including a mirror having a sphericalreflecting surfaca-an aspheric correcting :plate and a cathode ray tubehaving a target exposing surface, a correcting plate supporting meanscomprising a member having means to support the correcting platesubstantially at the "center of curvature of the spherical mirror, atube supporting member having a circular edge to contact the curved tubeface to provide support for the tube, a rod -'c0nnected to saidcorrecting plate supporting means and being axially adjustable thereon,a second rod rigidly-connected to said correcting plate supportingmeans, and a slot in said tube supporting member to receive said rigidlyconnected rod.

8. A cathode ray tube image projection device comprising an opticalsystem including a spherical mirror and a correcting plate locatedsubstantially at the center of curvature thereof to correct forspherical aberration, a housing having means defining a circle restingon thesph'erical light reflecting surface of said mirror, saidcorrecting plate being also centered on the axis of said housing toprovide alignment of said correcting plate with respect to said mirror,an electron image tube having -a surface comprising a light transmittingwindow so located relative to the housing and optical system that lightmay be directed in each direction between the tube and the sphericalmirror, a support for said tube surface so that the center thereof lieson the axis of said mirror which in turn coincides with the axis of saidcorrecting-plate means associated with said housing to provideaxial'adjustment of said tube, and guide means for cooperating with saidadjustable means for maintaining the tube window in aligned relationshipwith the spherical mirror and the correcting plate.

9. A projection device for use with a cathode ray tube comprising areflecting member, a housing having a circular edge for contacting aspherical surface of said reflecting member, a ring member forcontacting said reflecting memher on a surface opposed to that on whichsaid circular edge rests, said ring member having a flange, a flange onsaid housing disposed opposite the flange on said ring member, andfastening means for clamping said flanges.

10. The combination of an optical light receiving element having asubstantially spherical surface, a member having means defining a circleresting on said spherical surface whereby the center of curvature ofsaid spherical surface lies on the optical axis of both said member andsaid circle, a correcting plate, and supporting means for saidcorrecting plate coaxial with said circle to receive light reflectedfrom said substantially spherical surface.

11. In an image projection system including a mirror having a sphericalreflecting surface, an aspheric correcting plate and a cathode ray tubehaving a spherical target exposing surface, a correcting platesupporting means comprising a member having means to support thecorrecting plate substantially at the center of curvature of thespherical mirror, a tube support- REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 995,275 Miller June 13, 19112,128,791 Benford Aug. 30, 1938 2,161,368 McLeod June 6, 1939 2,245,257Crumrine June 10, 1941 2,273,801 Landis Feb. 17, 1942 2,353,898 NitschJune 18, 1944 2,400,916 Ceader May 28, 1946 2,404,943 Beshgeteor July30, 1946 2,415,211 Law Feb. 4, 1947

